Vodafone has chalked up its first big win in the corporate telecommunications market since sealing its takeover of TelstraClear in October.

The company said Bank of New Zealand, which has been a key TelstraClear customer for the past 10 years, had signed a contract with Vodafone to extend that for a further six years and expand the range of services it supplies to the bank.

The arrangement is understood to be worth tens of millions of dollars a year.

"This is a milestone partnership however you look at it," Vodafone chief executive Russell Stanners said in a statement.

"There are very few major organisations that have developed the mutual trust and expertise to work together so productively for so long."